Histocompatible bone marrow transplantation (BMT) is the treatment of choice for patients with relapsed acute lymphoblastic leukemia (ALL) and is effective therapy for patients with acute myelogenous leukemia (AML) and certain cases of ALL in first remission. At present BMT is restricted to 40% of patients who have a histocompatible family member as a possible donor. Histoincompatible BMT have been successfully performed in both dogs and rodents after the treatment of the donor bone marrow with T cell specific antibodies, either monoclonal or heteroantisera. Based upon these animal experiments, we propose to examine the feasibility of BMT with in vivo or in vitro monoclonal antibody treated haploidentical bone marrow. The antibody haploidentical transplants will be performed in patients with relapsed acute leukemia in resmission or severe combined immune deficiency. Using a monoclonal antibody to human T lymphocytes, OKT3, the efficacy of antibody treated haploidentical bone marrow transplants will be determined in terms of hematopoietic engraftment, immune reconstitution, and frequency and severity of acute and/or chronic graft versus host disease (GVHD). Patients with successful engraftment will be studied to determine the cellular basis of their stable chimerism and their immunocomppetence compared to recipients of histocompatible BMT. In particular we will examine the effect of recipient chimeric lymphocytes on the MLC and CML responses of donor lymphocytes to stored recipient cells. The effect of pretransplant chemotherapy and total body irradiation on the recipients capacity to remove heteroantiser coated autologous red blood cells and lymphocytes will be studied. The prophylactic use of intravenous OKT3 antibody as an immunosuppressant following transplantation will be compared to high dose standard therapy plus rabbit anti-human thymocyte serum (ATS). The successful use of OKT3 treated haploidentical bone marrow would permit the transplantation of the 60% of potential leukemic recipients who do not have a histocompatible donor.